Electric Pump

ABSTRACT

The present invention provides a compact electric motor, thus ensuring improved in-vehicle mountability. A pump is driven by an electric motor. The pump has a coil  14  disposed in a ring form around and along a stator core  13 . The stator core  13  has a plurality of claw magnetic poles which extend alternately from both ends of one member of the stator core  13  toward the end of the other member thereof. The electric motor drives the pump by rotating a rotor  16  disposed to face the inner periphery of the stator core  13  as the coil  14  is energized. The present invention provides a compact electric pump with no coil ends, thus ensuring improved in-vehicle mountability. Further, the present invention permits efficient cooling of the electric motor adapted to discharge a cooling medium. Still further, the present invention permits the use of a stator core made from a compressed powder core by molding with resin. In addition, the molded portion also serves as a partition separating pump and motor units.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electric pump driven by an electricmotor.

2. Description of the Related Art

Among measures to improve automobile fuel efficiency are firstly idlingstop adapted to stop an engine when a vehicle stops, and secondlyhybridization adapted to drive a vehicle using a rotary electric machineand an engine. These measures have already found commercial use. To usethese systems, a drive source is additionally required for a pump in thecase of an idling stop system because the engine stops when the vehiclestops. In the case of hybrid vehicles, on the other hand, a water pumpis required to cool the drive motor or starter-generator and itscontroller in addition to the idling stop system. As a result, anelectric pump using an electric motor is increasingly common as a drivesource.

JP-A-2000-213490 discloses an electric motor adapted to dischargecooling water by use of centrifugal force generated by rotating theimpeller with the output shaft of the electric motor.

SUMMARY OF THE INVENTION

The electric motor adapted to drive the water pump described inJP-A-2000-213490 has a coil wound around the stator core so that thecoil reciprocates along the drive shaft. As a result, the portionscalled the coil ends which do not contribute to generation of a statortorque protrude at both ends of the stator core. This makes itimpossible to reduce the axial length of the pump. As a consequence, thepump is large as a whole, resulting in poor mountability.

It is an object of the present invention to provide a compact electricpump with high mountability.

The present invention is characterized in that a pump structural body isdriven by an electric motor. The electric motor has a core with aplurality of first claw magnetic poles and a plurality of second clawmagnetic poles, each extending from both axial ends of one member of thecore toward the end of the other member of the core. The plurality offirst claw magnetic poles and the plurality of second claw magneticpoles are formed alternatively in the circumferential direction of thecore. A coil is wound around and along the core in a ring form.

The present invention is further characterized in that a pump structuralbody is provided adjacent to at least one end of the stator core and amagnetic pole member to discharge a cooling medium.

The present invention is still further characterized in that a pumpstructural body adapted to discharge a liquid is driven by an electricmotor. The electric motor includes a molded portion, which is formed bymolding of a non-magnetic material, at least on the inner periphery ofthe stator core which includes a compressed powder magnetic core.

The present invention makes it possible to reduce the size of anelectric motor as a whole because of absence of coil ends, thusproviding significantly improved mountability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of the axial side surface of an electricwater pump according to a first embodiment of the present invention;

FIGS. 2A to 2D are views describing in detail a stator core for onephase and a coil according the first embodiment of the presentinvention;

FIG. 3 is a sectional view along line A-A of the FIG. 1;

FIG. 4 is an explanatory view of a vehicle with the electric pump;

FIGS. 5A to 5C illustrate the electric water pump of a secondembodiment;

FIG. 6 is a sectional view of the axial side surface of the electricwater pump according to a third embodiment of the present invention;

FIGS. 7A and 7B are views describing in detail the stator core and thecoil according to the third embodiment of the present invention;

FIG. 8 is a diagram showing a control configuration according to thethird embodiment of the present invention;

FIGS. 9A to 9G are graphs illustrating the operating principles of thethird embodiment;

FIG. 10 is a sectional view of the axial side surface of the electricwater pump according to a fourth embodiment of the present invention;and

FIGS. 11A to 11D are views describing in detail the stator core of thefourth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of an electric water pump of the present invention will bedescribed with reference to the accompanying drawings.

First Embodiment

FIGS. 1 to 3 illustrate an electric motor of a first embodiment. FIG. 1is a sectional view of the axial side surface of the electric water pumpof the first embodiment. FIGS. 2A to 2D are views describing in detail astator core for one phase and a coil of the first embodiment. FIG. 2A isa perspective view of the partial section of the stator core and thecoil. FIG. 2B is a front view of the stator core. FIG. 2C is a developedview, in the circumferential direction, of the inner periphery of thestator core as seen from the inside. FIG. 2D is a sectional view of thepartial side of the stator core and the coil. FIG. 3 is a sectional viewalong line A-A of FIG. 1.

The electric water pump is designed primarily for use in hybrid vehiclesdriven by an engine and a drive electric motor in combination so as tocool the drive electric motor or the starter-generator and itscontroller and other devices.

In FIG. 1, a water pump unit 1 as a pump structural body uses acentrifugal pump. The water pump unit 1 includes a pump housing 3 with apump chamber 2 and an impeller 4 rotatably housed in the pump chamber 2.

The pump housing 3 is formed by die-casting with an aluminum alloy, ametallic material with high thermal conductivity. As shown in FIG. 3,the pump chamber 2 is formed inside the pump housing 3 so that the innerdiameter thereof increases gradually depending on the circumferentialposition. As a result, the pump housing 3 is divided axially into twomembers or members 3A and 3B. The members 3A and 3B are combined into asingle piece by bolts 6 after the insertion of the impeller 4 and adrive shaft 5. Further, as shown in FIG. 1, a tubular suction portion 7is formed to project outward from the approximate center of the pumpchamber in the axial direction. A tubular bearing support portion 8 isformed to project toward an electric motor unit 11 from the approximatecenter of the pump chamber in the axial direction. Further, as shown inFIG. 3, a discharge portion 9 is formed near the position where theinner diameter of the pump chamber 2 is largest. It is to be noted thata flowing medium discharged from the discharge portion 9, or morespecifically cooling water as a cooling medium, is a freeze-resistantliquid (antifreeze) prepared by adding ethylene glycol to water, withits anticorrosion effect also improved. This cooling water is suppliedto the drive electric motor and its inverter of a hybrid vehicle.

The impeller 4 in the pump chamber 2 includes an umbrella disk-shapedplate on the side of the suction portion 7, an umbrella disk-shapedplate on the side of the electric motor unit 11, and a plurality ofblades (eight blades in the present embodiment) arranged radiallytherebetween. The impeller 4 is integrally molded by injection moldingwith resin material. A hole 10 is provided at the approximate center ofthe impeller 4. The metal drive shaft 5 in a hollow cylindrical form ispress-fitted into the hole 10 and secured in place so that the driveshaft 5 and the impeller 4 rotate integrally.

With the water pump unit 1 thus constructed, the impeller 4 rotates asthe drive shaft 5 rotates, permitting cooling water scraped out by theblades to flow to the outer peripheral side by centrifugal force.Cooling water thus permitted to flow to the outer peripheral side isguided along the inner peripheral surface of the pump chamber 2 into thedischarge portion by inertial force. It is to be noted that negativepressure is present in the proximity of the suction portion 7 becausecooling water on the impeller 4 flows to the outer peripheral side. As aresult, cooling water flows in through the suction portion 7. Therefore,the pump chamber 2 is filled with cooling water at least during therotation of the impeller 4.

Next, a description will be made of the electric motor unit 11 providedadjacent to the water pump unit 1 with reference to FIG. 1 and FIGS. 2Ato 2D.

The electric motor unit 11 includes a motor housing 12 having a housingportion therein and stator cores 13 as cores, housed in the motorhousing and adapted to generate a magnetic field as they are energized.The electric motor unit 11 also includes coils 14 housed in the statorcores 13 and a rotor 16 as a magnetic pole member having permanentmagnets 21 arranged to be opposed to the stator.

The motor housing 12 has a housing portion 12 a in a hollow cylindricalform and a sealing plate 12 b adapted to seal one end of the housingportion 12 a. The two portions are combined into one piece by bolts 15.Further, the opening at the other end of the housing portion 12 a issealed with the pump housing 3 by the bolts 6. As a result, part of thepump housing 3 also serves as the motor housing 12. It is to be notedthat the housing portion 12 a and the sealing plate 12 b are formed bydie-casting with aluminum alloy as with the pump housing 3. The sealingplate 12 b has a bearing support portion 17 in a hollow cylindrical formwhich projects toward the side of the water pump unit. The bearingsupport portion 17 is integrally molded as with the bearing supportportion 8 of the pump housing 3 so as to be opposed to the bearingsupport portion 8.

The inner periphery of the bearing support portion 8 of the pump housing3 and that of the bearing support portion 17 of the motor housing 12have each a large and small diameter portions formed axially in astepped form. Resin bushings 18 as bearings, that is to say slidingbearings, are press-fitted into the large diameter portion. The bushings18 are axially positioned as they touch the small diameter portion.Further, these bushings 18 have each a disk-shaped flange portion whichis integrally molded at the end on the side where the two bushings faceeach other.

Next, the stator core 13 and the coil 14 will be described. In thepresent embodiment, a three-phase brushless motor is used which has thestator cores 13 for three phases and the coils 14. Therefore, the threestator cores 13, each housing the coil 14, are disposed in a laminatedfashion and electrically insulated from one another in the motor housing12 so as to be arranged side by side in the axial direction.

A description will be made of one of the three phases. The stator core13 includes a ring-shaped member divided into two members at theapproximate center in the axial direction. One of the two ring-shapedmembers is in the form of a claw tooth (claw magnetic pole). Morespecifically, this member includes an outer peripheral portion 13 awhich extends axially on the outermost periphery and a hollowdisk-shaped circular portion 13 b which is provided at the end of theouter peripheral portion. The member also includes a plurality of clawbase portions 13 c (12 portions in the present embodiment) which extendfrom the circular portion toward the inner periphery approximately atequal intervals therebetween and a plurality of claw portions 13 d whichextend axially from the claw base portions 13 c toward the counterpartring-shaped member in a tapered shape, that is to say approximately in atrapezoidal shape.

As shown in FIGS. 2A and 2D, the stator core 13 is formed so that thecross section thereof is approximately in the shape of letter U. Theclaw portion 13 d is longer than the outer peripheral portion 13 a. Theclaw portions 13 d and the claw base portions 13 c are connectedcontinually on the inside in the shape of a circular arc. It is to benoted that the claw pole includes the claw base portion 13 c and theclaw portion 13 d.

The two ring-shaped members of substantially the same shape thusconstructed are combined into the stator core 13 for one phase bymolding. In the molding, the two members are arranged to be opposed toeach other so that the claw portions 13 d of the two members aredisposed alternately. Then the entire surface other than the clawportions 13 d is molded with a non-magnetic resin material 19. In thisprocess, the coil 14 is placed thereinside which is wound around thering-shaped members in the shape of a circular arc (in a toroidalshape). It is to be noted that the coil 14 is insulation-coated. It isalso to be noted that the two ends thereof are drawn out from theopposed surfaces of the ring-shaped members for energization andconnected to an inverter for current control.

In hybrid and other vehicles, a high supply voltage is used, making itnecessary to dispose an insulator between the coil 14 and the statorcore 13. If a low supply voltage is used (as low as 12V in ordinaryautomobiles), however, the coil 14 may be disposed directly on thestator core 13.

It is to be noted that since the present embodiment uses a three-phasemotor, the stator cores 13 of phases U, V and W are housed in the motorhousing 12 by press-fitting and secured in place. In the motor housing12, the stator cores 13 are arranged side by side in the axial directionso that the claw portions 13 d are shifted in the circumferentialdirection by an electrical angle of 120 degrees. The coils 14 are eachconnected to a three-phase inverter. On the other hand, since the clawportions 13 d are spaced apart in the circumferential direction by anelectrical angle of 120 degrees, the coils 14 of the three phases can bewound in the same direction. As a result, all the stator cores 13 can beconstructed with completely identical components. It is to be noted thatthe stator cores 13 have each a resin material molded on the surface.Therefore, each thereof is attached in insulated fashion to the motorhousing 12. However, a space is formed between the pump housing 3 andthe sealing plate 12 b of the motor housing 12.

The aforementioned stator cores 13 are each made from a compressedpowder core formed by compression molding of iron powder which is amagnetic powder coated with a non-magnetic substance. Higher strengthcan be achieved by causing a binding agent to reside between iron powderparticles.

On the other hand, a space is provided between the claw magnetic polesof the two ring-shaped members of the stator core 13 to reduce theinductance of the coil 14, as shown in FIG. 2C. The non-magnetic resinmaterial 19 is also molded in the space between the claw magnetic poles.The resin material 19 is not molded on the inner peripheral surface ofthe claw portions 13 d. As a result, the resin material 19 and the clawportions 13 d are arranged alternately on the inner peripheral surfaceof the stator core 13.

Next, the rotor 16 as a magnetic member will be described. The rotor 16includes the drive shaft 5 secured to the impeller 4 so as to beintegrally rotatable, a rotator core 20 secured to the drive shaft 5 andpermanent magnets 21 disposed on the outer periphery of the rotator core20. The rotator core 20 is formed by integral molding of a cylindricalmagnet attachment portion 20 a which is disposed on the outer peripheryand a drive shaft attachment portion 20 b using a magnetic steelmaterial. The drive shaft attachment portion 20 b is narrower than themagnet attachment portion 20 a and disposed at the approximate center ofthe same 20 a. In other words, the two portions are molded so that theaxial cross-section is approximately in the shape of letter H. Further,a hole 20 c is formed on the inner periphery of the drive shaftattachment portion 20 b. As the drive shaft 5 is press-fitted into thehole 20 c, the rotator core 20 and the drive shaft 5 are securedtogether so as to be integrally rotatable. Still further, the pluralityof rod-shaped permanent magnets 21 extending in the axial direction aresecured in the circumferential direction on the outer periphery of themagnet attachment portion 20 a. The permanent magnets 21 are arranged sothat the magnetic poles of every two adjacent magnets are different fromeach other.

The rotor 16 thus constructed is disposed so that the inner peripheriesof the stator cores 13 and the permanent magnets 21 are opposed to eachother. The drive shaft 5 is rotatably supported by the two bushings 18.The drive shaft 5 is prevented from moving in the axial direction byflange portions of the two bushings 18.

Further, cooling water is introduced toward the rotor 16, for example,through the gap between the drive shaft 5 and the pump housing 3, alongthe inner periphery of the drive shaft 5 and through the gap between theinner periphery of the bushings 18 and the outer periphery of the driveshaft 5. As a result, the rotor 16 rotates in cooling water. At thistime, cooling water is constantly introduced between the bushings 18 andthe drive shaft 5, thus allowing to construct smooth sliding bearings.

Next, the operation of the electric motor unit 11 thus constructed willbe described below.

The coils 14 are supplied with current from a power source such asbattery via the three-phase inverter. As a result, different magneticpoles are generated on first and second claw magnetic poles, the firstclaw magnetic pole extending from one of the ring-shaped member of thestator core 13, the claw magnetic pole extending from the otherring-shaped member. For example, if N pole is generated on the firstclaw magnetic pole, S pole is generated on the second claw magneticpole. In the present embodiment, the coils 14 have the phases U, V andW. This makes it possible to regulate energization of each of the coils,thus switching the magnetic poles as if they rotate. As a result, thepermanent magnets 21 on the rotor 16 which are opposed to the clawmagnetic poles move in the rotational direction together with magneticfields generated by the claw magnetic poles. This causes the rotor 16 torotate. It is to be noted that the rpm of the drive shaft 5 can becontrolled by controlling the energization of the coils 14 of the phasesU, V and W.

To control the rotation of the rotor 16, detection of the position ofthe same 16 is normally required by a magnetic pole position detector.However, the present embodiment uses the induced voltage positiondetection method adapted to detect the magnetic pole position from thevoltage induced in the coil 14, thereby switching the energization ofthe coils 14 of the three phases. That is to say, the present embodimentuses a sensorless method to detect the position of the rotor 16. It isto be noted that the load change of the impeller 4 of the water pumpunit is slow. As a result, the use of such a method is sufficientlypossible.

Although the present embodiment has been described to cool the driveelectric motor or the starter-generator and its controller in hybridvehicles, the invention may be used as a pump to cool the engine or warmthe cabin. Here, a vehicle with the electric pump will be described withreference to FIG. 4. A hybrid vehicle will be described as an example.

In FIG. 4, the engine room of a vehicle 22 has an engine 23 coupled viaa transmission (not shown) to wheels 24 which drive the vehicle. Here,cooling water supplied by a first electric pump 25 removes heat from theengine 23 to cool the engine 23. Cooling water is cooled down as itreleases heat removed from the engine 23 via a thermostat 26 to aradiator 27 and returns to the first electric pump 25. On the otherhand, cooling water supplied by a second electric pump 28 cools aninverter 29 and a traveling motor 30. Then cooling water is cooled downby the radiator 27, shared by cooling water from the first electric pump25, and returns to the second electric pump 28. Further, cooling watersupplied by a third electric pump 31 is introduced into part of coolingwater circulated by the first electric pump 25 to release heat from theengine 23 into the cabin by a cabin heater 32 and returns to theoriginal flow path. It is to be noted that a bypass channel 33 isprovided to allow the cooling medium to bypass the radiator 27 if thethermostat 26 determines that the engine 23 has not warmed up.

Next, the operation and effects of the present embodiment will bedescribed.

In the present embodiment, the coils are wound around and along thecores in a ring shape, thus eliminating coil ends which would otherwisenot contribute to generation of a torque. This makes it possible tobring the cores and the pump structural body closer together to theextent possible, thus permitting size reduction and thereby providingimproved mountability.

It is to be noted that when these pumps are mounted in a vehicle, theengine room which will accommodate the pumps is a crowded space with avariety of parts housed therein. In particular, recent years have seen adrastic increase in the number of parts mounted in the engine roombecause, for example, of hybridization and functional improvement. As aresult, there is a growing tendency to require the parts accommodatedtherein to be smaller and lighter than parts accommodated in otherrooms. In light thereof, it is extremely beneficial to use pumps asthose described above.

Such electric pumps are finding wider use as shown in FIG. 4. Thesepumps have two advantages. One of the advantages is that the pumpsoccupy a smaller space in the engine room thanks to size reduction. Theother advantage is that the inverter and the traveling motor of hybridvehicles can be reduced in size because of higher power output of theelectric pumps, thus contributing to improved layout flexibility and, ina broader sense, improved vehicle performance. Thus, these electricpumps are advantageous not only as pumps alone but also in terms of thevehicle as a whole.

In addition, the coils are easy to be manufactured. Besides, they areeasier to be molded after being wound around the cores as compared tocoils wound around laminated cores. This ensures a high proportion ofspace occupied by the coils in the coil housing space, thus reducingcoil resistance and thereby providing a motor with high efficiency.Further, improved occupancy ratio ensures reduced thermal resistancebetween the coils and cores, thus rendering the drive motor capable ofwithstanding a large load. Conversely these advantages can be takenadvantage of to reduce the size and weight of the motor. Still further,the length of one turn of coil can be reduced, thus providing reducedresistance and ensuring higher motor efficiency.

In the present embodiment, multiphase cores are used, ensuring easy andpositive control.

In the present embodiment, the pump structural body is disposed adjacentto at least one end of the core and magnetic pole member so that thepump structural body discharges a cooling medium. This ensures effectivecooling of the cores and magnetic member.

In the present embodiment, no coil end is present, making it possible toprovide a pump housing at one axial end of the motor housing. Thisimproves the cooling effect. In this case, other effects can also beachieved, including reduction in parts, size reduction and weightreduction.

In the present invention, the pump and motor housings are molded withthe same material, thus ensuring efficient cooling. In particular, theuse of aluminum alloy, a material with high thermal conductivity,provides added cooling effect.

In the present embodiment, the bearings of the magnetic pole member aredisposed along the inner periphery of the magnetic pole member. Thisprovides a shorter axial length of the pump while securing appropriatebearing lengths, thus contributing to size and weight reduction. Inparticular, the rotor core as a magnetic member has a large enoughmargin in terms of magnetic flux produced. Therefore, it is possible toreduce the axial length of the pump and dispose the sliding bearingsinside the rotor.

In the present embodiment, the cores are made of compressed powdercores, thus allowing easy manufacture of complicated three-dimensionalshapes. Further, the compressed powder core is one piece as a whole incontrast to a conventional laminated core manufactured by punching outthin steel sheets. As a result, this core is structurally rigid anddifficult to vibrate, thus keeping noise low. When constructed in theaforementioned shape, the core can be made into a motor offering furtherreduced vibration and noise. Still further, the core can be molded witha necessary raw material, thus providing a material utilization ratio of100% and keeping manufacturing cost low.

In the present embodiment, the stator cores as cores are molded with anon-magnetic material, thus providing enhanced strength even if thestator cores are made from compressed powder cores. Further, the corescan be improved in durability so as to prevent corrosion of the coils ascooling water as liquid is introduced therein. Still further, the statorcores can be readily sealed so as to prevent external cooling waterleakage. As a result, there is no need to provide a cooling mediumshield separately between the stator cores and the rotor as isconventionally practiced. Instead, the stator cores can be formeddirectly on the stator surfaces facing the rotor. This reduces themagnetic gap, thus preventing a reduction of torque resulting from anincreased gap length due to the presence of a shield, that is to say lowefficiency and other problems. Therefore, not only size and weightreduction but also high efficiency can be achieved. In particular, theuse of resin, a non-magnetic material, will prevent corrosion and otherproblems caused by cooling water.

In the present embodiment, the inner peripheral surfaces of the statorcores are constructed so that the non-magnetic material and the magneticpoles are formed alternately in the circumferential direction. Thisallows the stator cores to be located on the stator surfaces facing therotor, thus reducing the magnetic gap length and providing improvedmotor characteristics. Further, enhanced cooling effect of the statorcores will be achieved.

In the present embodiment, cooling water as cooling liquid is introducedinto the stator cores and the ends thereof. This ensures efficientcooling of not only the stator cores and coils but also the rotor withcooling water. Such an effective removal of heat also allows for acompact, lightweight and highly efficient construction. Further, therotor is supported by bearings in cooling water, allowing for smoothsupporting of the rotor with inexpensive sliding bearings. Inparticular, the drive shaft is hollow so that cooling water is readilyintroduced into the two bearings, thus ensuring further smoothsupporting of the rotor.

In the present embodiment, the claw portions of the cores are inclinedin a tapered shape. This reduces cogging torque of the motor and bringsthe waveform of the coil induced voltage closer to a sine wave. As aresult, supplying a sine wave current produces a constant torque fromthe three phases with minimum pulsation in the rotational direction.This provides low motor noise.

Thus, in the present embodiment, an electric water pump has beendescribed as an example of electric pump. The present invention is alsoapplicable, for example, to a power steering pump adapted to supply oilto a hydraulic power steering system, oil pumps such as lubricating pumpadapted to supply lubricating oil to the engine, a compressor which usesa gas as its cooling medium and an electric oil pump which uses oil asits cooling medium. However, the present invention is more useful foruse as a pump adapted to discharge a cooling medium as it is capable ofefficiently cooling the electric motor unit. It is to be noted that thepump unit need not necessarily be a centrifugal pump. Instead, it may bea vane pump, gear pump, plunger pump, and so on.

In the present embodiment, the pump and motor housings are formed withthe same material. The two housings share a part thereof. However, thetwo housings may be formed with different materials and separately. Thisallows for selection of materials suited for application. The pump andmotor housings need not necessarily be made of a metallic material.Selection of a resin material is also possible. A resin material withhigh thermal conductivity such as unsaturated polyester will provideeffective cooling.

In the present embodiment, an impeller made of a resin material is used.However, the impeller may also be formed by metal stamping, die-castingor casting of a metallic material. This will enhance the impellerstrength.

In the present invention, the impeller and the drive shaft areconstructed with separate members. However, they may be integrallymolded. This will reduce the parts count.

In the present embodiment, metal bushings are used to support the driveshaft. However, resin bushings may also be used. Further, needle or ballbearings may also be used. It is to be noted that if needle or ballbearings are used, they should be kept away from cooling water to theextent possible. A seal is required to prevent cooling water fromflowing back and forth between the pump unit and the electric motorunit. In this case, the rotor does not rotate in cooling water, but doesin air. It is preferable that grease or other lubricating oil be appliedto the bearings for lubrication.

In the present embodiment, the cores remain stationary whereas the rotorwith permanent magnets as magnetic members rotates. However, a so-calledDC motor may also be used in which the core rotates as the rotor as thecoil is supplied with current from a brush whereas the permanent magnetsremain stationary as the stator. Further, a so-called induction motormay also be used in which a separate core and coil are used in place ofthe permanent magnets.

In the present embodiment, the stator cores are made from compressedpowder cores. However, the stator cores may be formed by cutting orstamping. The cores formed by such processes can be enhanced in strengthas compared to compressed powder cores.

In the present embodiment, the non-magnetic material and the magneticpoles are formed alternately on the inner peripheries of the statorcores in the circumferential direction. However, the entire innerperipheries of the same may be molded. This will prevent corrosion ofthe stator cores caused by cooling water.

In the present embodiment, the electric motor unit and the controllerthereof such as inverter are provided separately. However, they may beformed integrally and disposed at the end of the motor housing on theside opposite to the pump housing. This will provide an electric motorof more compact construction.

In the present embodiment, the induced voltage position detectionmethod, a sensorless method, is used to detect the rotor position.However, the provision of a magnetic pole position detector will providea reduced startup time.

In the present embodiment, the stator cores are molded phase by phase,after which they are secured in the motor housing. However, the statorcores may be secured in the motor housing first and then molded togetherwith the motor housing.

In the present embodiment, a resin molded portion and a space areprovided between the stator cores and the pump housing. However, if thepump housing is made of a non-magnetic material such as aluminum alloy,the stator cores and the pump housing may be directly in contact witheach other. This allows heat from the coils to directly escape to therefrigerant via the pump housing, thus providing enhanced cooling effectand permitting size and weight reduction. Further, the resin moldedportion may be eliminated so that only a space is provided between thestator cores and the pump housing. If, as a result of this construction,the refrigerant can be brought in direct contact with the side surfacesof the stator cores, heat will be able to escape directly from thestator windings via the stator cores to the refrigerant, thus permittingfurther size reduction.

In the present embodiment, the stator cores of the phases U, V and W arespaced apart in the circumferential direction by an electrical angle of120 degrees. However, the stator cores may be spaced apart in thecircumferential direction by an electrical angle of 60 degrees. In thiscase, the phase sequence is U, W and V. The coil of the phase W at thecenter must be wound in the reverse direction.

In the present embodiment, the claw portions of the cores are inclinedin a tapered shape. However, they may be parallel to each other in theaxial direction.

Second Embodiment

FIGS. 5A to 5C illustrate the electric water pump of a secondembodiment. FIG. 5A is a sectional view of the axial side surface of theelectric water pump as the second embodiment. FIG. 5B is a sectionalview along line B-B of FIG. 5A. FIG. 5C is a side view of only thestator cores molded with a resin which is a non-magnetic material. It isto be noted that the same parts as those in the first embodiment aretermed the same names and denoted by the same reference numerals.

The second embodiment differs from the first embodiment in that themolded portion 19 of the stator cores 13 molded with a resin, anon-magnetic material, is provided with channels 34 through whichcooling water as a cooling medium can flow.

As shown in FIG. 5B, the channels 34 include channels 34 a, 34 b and 34c. The channel 34 a is an annular channel provided in an annular shapeat the approximate center of the circular portion in the direction ofradius on the axial end surface of the stator cores 13. The channels 34b are radial channels provided radially, each located at the center ofone of the magnetic poles, that is to say at the approximate center ofeach of the claw base portions 13 c in the circumferential direction.The channels 34 c are axial channels as shown in FIG. 5C, each extendingfrom each of the radial channels approximately in the axial direction onthe axial side surfaces of the stator cores 13. The channels 34 areformed on the two end surfaces and the side surfaces of the stator cores13 of the three phases. These channels are molded by the mold used forinjection molding of resin. Each of the stator cores 13 has the samechannels as the other cores. As a result, when the stator cores 13 ofthe three phases are axially arranged side by side, the identicallyshaped annular and radial channels 34 a and 34 b of the adjacent coresare brought face to face. The channels 34 c of the adjacent cores arealso located at the same positions, permitting communication between thechannels 34 c.

As described above, in the present embodiment, the channels 34 permitcooling water to fill into the inner peripheral sides of the statorcores 13, thus providing improved cooling effect.

In the present embodiment, some radial channels are provided, thusensuring effective distribution of cooling water.

In the present embodiment, some channels are provided between the statorcores, thus allowing for cooling of each of the cores.

In the present embodiment, some channels are formed, each at the centerof one of the magnetic poles, thus allowing for cooling of the locationsmost needed to be cooled.

In the present embodiment, the molded portion of each of the statorcores has annular and axial channels. As a result, cooling can beaccomplished between the stator cores, between the stator cores and thepump housing and between the stator cores and the motor housing. Thispermits distribution of the refrigerant all around the electric motor,thus providing further improved cooling effect and an even more compactmotor.

In the present embodiment, the rotor is rotatably disposed to face theinner peripheries of the stator cores. As a result, when the rotor rpmis high, cooling water flows into the areas of the inner peripheries ofthe stator cores opposed to the rotor. The pressure drops with increasein flow rate. This creates a pressure difference between the pumphousing and motor housing sides of the stator cores not opposed to therotor. As a result, cooling water circulates through the channels. Thisprovides further improved cooling effect.

In the present embodiment, the channels provided on all the moldedportions of the stator cores are identically shaped. This permitsmolding of the channels with a single mold, thus providing aninexpensive pump.

In the present embodiment described above, the channels are formed witha mold. However, the channels may be formed by cutting.

In the present embodiment, annular channels are provided. However, ifthese channels are omitted, all the channels can be formed by moldingthe plurality of stator cores in a single step.

Third Embodiment

FIG. 6 and FIGS. 7A and 7B illustrate the electric water pump of a thirdembodiment. FIG. 6 is a sectional view of the axial side surface of theelectric water pump of the third embodiment. FIGS. 7A and 7B are viewsdescribing in detail the stator core and coil of the third embodiment.FIG. 7A is a perspective view of the partial section of the stator coreas a core and the coil of the third embodiment. FIG. 7B is a front viewof the stator core. It is to be noted that the same parts as those inthe first embodiment are termed the same names and denoted by the samereference numerals.

The third embodiment differs from the first embodiment in that asingle-phase motor is used which includes the single-phase stator core13. The third embodiment also differs in that a stepped portion 35 isprovided on one circumferential side of each of the claw portions 13 dof the claw magnetic poles. The third embodiment also differs in that aposition detector 36 is provided to detect the rotor position.

The stator core 13 is almost identical to one of the stator cores 13extracted from the first embodiment. In the former stator core 13,however, each of the claw portions 13 d of the claw magnetic polesextending from both ends of the stator core 13 has the stepped portion35, as shown in FIGS. 7A and 7B. The stepped portions 35 are provided asmagnetic field deviation portions to deviate a magnetic field in onecircumferential direction. These portions are provided on the same sideso that one circumferential side is farther from the rotor than theother circumferential side. The stepped portions 35 each have a step atthe approximate center in the circumferential direction of the clawportion.

As shown in FIG. 6, the position detector 36 is installed in a depressedportion which is provided on the inside at the end of the motor housing12 on the side opposite to the pump. The position detector 36 detectsleak magnetic flux of the permanent magnet 21 on the rotor 16, thusdetecting the position of the permanent magnet 21, that is to say theposition of the rotor 16.

Next, a description will be made of the control configuration of thesingle-phase motor of the third embodiment with reference to a controlconfiguration diagram of FIG. 8.

In FIG. 8, the single-phase motor includes the electric motor unit 11, aconverter CONV adapted to supply AC power from a DC power supply Edc tothe electric motor unit 11, and a control circuit CONT adapted tocontrol the converter CONV.

Here, the control circuit CONT includes an angle converter A whichconverts the output from the position detector 36 into angleinformation, a speed control circuit B, and a converter output circuitC. In this configuration, the angle converter A receives informationabout leak magnetic flux of the permanent magnet 21 from the positiondetector 36 and outputs rotor position information based on the receivedinformation. Measuring the period of electric angle in a half cycle ofthe output signal from the position detector 36 makes it possible todetermine the rotor position information and the energization direction,that is to say whether to turn on positive or negative switching devicesof the converter CONV. The speed control circuit B calculates an errorspeed based on an externally given speed command Ns and theaforementioned speed information. The speed control circuit B submitsthe error to proportional-integral and other control before sending acontrol output to the converter output circuit C. This allows to controlthe converter CONV including an H bridge, thus controlling the speed tothe target speed specified by the speed command Ns.

The above control is intended for fans and pumps. The response frequencyfor this control is extremely low or several hertz or less. As a result,the control is performed in a stable manner.

Next, a description will be made of the operating principle and theoperation at constant rotation speed of the single-phase motor of thethird embodiment with reference to waveforms in FIGS. 9A to 9G.

In the waveforms of FIGS. 9A to 9G, the horizontal axis represents aposition θ of the rotor 16 in the range from 0 to 360 degrees inelectrical angle. FIG. 9A illustrates an output signal of the positiondetector 36. FIG. 9B illustrates a voltage Vt (θ) applied to the coil 14of the electric motor. FIG. 9C illustrates a voltage V0 (θ) inducedacross the coil 14 by the magnetic flux of the permanent magnet 21. FIG.9D illustrates a coil current iw (θ). The coil current iw (θ) isdetermined by the voltage Vt (θ) in FIG. 9B, the induced voltage V0 (θ)in FIG. 9C, and a resistance r and an inductance L of the coil 14 usingthe following formula:Vt(θ)=(r+p)iw(θ)+V0(θ)  (1)

where ps is d/dt.

FIG. 9E illustrates a cogging torque Tc (θ) generated between the statorcore 13 and the permanent magnet 21 when there is no current flow. FIG.9F illustrates a torque T0 w (θ) generated by the induced voltage andthe coil current. An output P0 w (θ) expressed by the product of theinduced voltage V0 (θ) in FIG. 9C and the current iw (θ) in FIG. 9Drepresents the output produced by the magnetic flux of the permanentmagnet 21 and the coil current. If an angular velocity ω of the rotor 16is constant, the torque T0 w (θ) is given by the following formula:T0w(θ)=P0w(θ)/ω  (2)

FIG. 9G illustrates a total torque T (θ) of the electric motor. Thistorque is the sum of the torque T0 w (θ) generated by the inducedvoltage and the coil current and the cogging torque Tc (θ) and given bythe following formula:T(θ)=T0w(θ)+Tc(θ)  (3)

If the angular velocity ω of the rotor 16 is constant, the total torquewill have the same waveform as the output torque.

The cogging torque of the single-phase motor exhibits a waveform asshown in FIG. 9E relative to the rotating position because of thestepped portions intentionally provided only on one side of the surfaceof each of the claw portions 13 d of the stator core 13. Next, adescription will be made of the torque T0 w (θ) generated by the inducedvoltage and the coil current. The torque T0 w (θ) makes up the maintorque of the single-phase electric motor. First, the induced voltagegenerally exhibits a rectangular waveform as shown in FIG. 9C. If thepolarity of the applied voltage is switched at the zero-cross point ofthe output signal of a Hall device, as shown in FIG. 9A, which isdisposed at a position slightly leading the induced voltage (the outputsignal of the Hall device is shaped into a sine wave by moving the Halldevice away from the permanent magnet), the voltage as shown in FIG. 9Bis applied to the coil 14. As a result, the current shown in FIG. 9Dflows, causing a torque to be generated by the current flowing into thecoil 14 and the voltage induced thereacross as shown in FIG. 9F. Thisoutput exhibits the waveform as shown in FIG. 9F as the induced voltagedips twice to near zero over a range of 360 degrees in electric angle.These voltage dips occur due to the operating principle of thesingle-phase drive motor. If these dips and the positive components ofcogging torque are added together, a nearly uniform torque can beproduced as a whole.

As described above, the motor of the present embodiment is asingle-phase motor, allowing for significant reduction in parts countand thereby making the pump inexpensive. Further, although not producinga uniform torque as by a three-phase motor, the single-phase motor canbe rendered capable of producing a comparably flat torque. This torquenon-uniformity can be eased by changing the angle by which the appliedvoltage leads the induced voltage and by changing the applied voltagewaveform. These changes can be accomplished by causing the appliedvoltage to increase smoothly at the leading edge and to declinegradually at the trailing edge. Another factor involved is conformitybetween the cogging torque waveform and that of the torque generated bythe induced voltage and the coil current. The output torque can be madeflat relative to the rotor angle θ by generating the cogging torqueoptimally in the recessed position on the claw portion surface.

In the present embodiment, an H-bridge control circuit can be used, thusreducing the number of switching devices to only two. This ensuressimple circuit configuration including gate circuits, providing acontroller configured at low cost.

As described above, in the present embodiment, the stepped portions areprovided on the claw portions as magnetic field deviation portions.However, these portions need not be stepped as long as onecircumferential side thereof is farther from the rotor than the othercircumferential side thereof. For example, one circumferential side ofthe claw portion may be smoothly thicker than the other circumferentialside thereof. Further, the claw portion thickness in the circumferentialdirection may be the same. In this case, a material highly permeable tomagnetic flux may be provided on one circumferential side of the clawportion, and a material not highly permeable on the othercircumferential side thereof. Still further, the claw portion may bemade of different materials in the circumferential direction so as tochange the amount of passing magnetic flux in the circumferentialdirection. These constructions eliminate steps, ensuring a longer moldlife.

Fourth Embodiment

FIG. 10 and FIGS. 11A to 11D illustrate the electric water pump of anfourth embodiment. FIG. 10 is a sectional view of the axial side surfaceof the electric water pump of the fourth embodiment. FIGS. 11A to 11Dare views describing in detail the stator core as a core of the fourthembodiment. FIG. 11A is a front view of the stator core for one phase.FIG. 11B is a side view of the stator core for one phase. FIG. 11C is arear view of the stator core for one phase. FIG. 11D illustrates thestator cores for three phases as they are positioned in the rotatingdirection and laminated together. It is to be noted that the same partsas those in the first embodiment are termed the same names and denotedby the same reference numerals.

The fourth embodiment differs from the first embodiment in that theaxial ends of the stator cores 13 are in close contact with the motorhousing 12, and that a rotation stop mechanism is provided to restrictthe relative rotation of the stator core 13 or the motor housing 12adjacent to the axial end of each of the stator cores 13.

As shown in FIGS. 11A and 11B, the circular portion 13 b on the side ofthe axial pump chamber 2 in the stator core 13 has recessed portions 37which make up part of the rotation stop mechanism. The recessed portions37 are provided as three grooves formed radially on both circumferentialsides of each of the two adjacent claw base portions 13 c. It is to benoted that the circumferential angle formed by the recessed portions 37is such that the stator cores are spaced apart in the circumferentialdirection by an electrical angle of 120 degrees.

As shown in FIGS. 11B and 11C, a projected portion 38 which makes up therotation stop mechanism together with the recessed portions 37 is moldedintegrally on the circular portion 13 b on the side of the sealing plate12 b in the stator core 13. The projected portion 38 is located at theback of the recessed portion 37 in the middle of the three recessedportions 37 arranged in the circumferential direction. The projectedportion 38 is provided engageably with the recessed portion 37 and hasapproximately the same shape as the same 37.

Further, as shown in FIG. 10, the sealing plate 12 b as the motorhousing 12 has the recessed portion 37 which is provided engageably withthe projected portion 38 of the stator core 13 at one circumferentiallocation. A housing 3 b which serves both as the motor and pump housingsalso has the projected portion 38 which is provided engageably with therecessed portion 37 of the stator core 13 at one circumferentiallocation. It is to be noted that the recessed portions 37 and theprojected portions 38 are formed almost in the same shape.

In the engagement of the recessed portions 37 with the projectedportions 38 thus provided, the projected portion 38 of one of the statorcores 13 engages with the circumferentially outer one of the threerecessed portions 37 of the adjacent stator core 13 as shown in FIG.11D. Further, the recessed portion 37 of one of the stator cores 13engages with the projected portion 38 of the housing 3 b which servesboth as the motor and pump housings. Still further, the projectedportion 38 of one of the stator cores 13 engages with the recessedportion 37 of the sealing plate 12 b.

As described above, in the present embodiment, the stator cores for theplurality of phases are positioned in place by the rotation stopmechanism, thus permitting positive and easy positioning of the statorcores to a position corresponding to the desired electrical angle.

In the present embodiment, the rotation stop mechanism includes therecessed and projected portions, providing increased contact area withthe motor housing. This ensures heat removal from the motor housingwhich is cooled by the adjacent pump structural body, thus providingimproved cooling effect. Particularly in the present embodiment, therecessed portions include grooves. As a result, the projected portionscan be formed long in a rectangular shape, allowing for easier heattransfer.

In the present embodiment, the plurality of recessed portions areprovided on each of the stator cores. This allows for positioning of thestator cores to a circumferential position appropriate to the desiredelectrical angle, thus providing improved productivity.

As described above, in the present embodiment, the rotation stopmechanism includes the recessed and projected portions. However,separate members may be attached to the stator cores to stop therotation.

In the present embodiment, the recessed portions include grooves, andthe projected portions rectangular protrusions. However, the recessedportions may include holes, and the projected portions circularprotrusions. In this case, the area of the recessed and projectedportions is smaller. However, this construction will reduce the impacton the magnetic circuit.

In the present embodiment, the stator cores have the same shape.However, the stator cores may have the projected and recessed portionsat different positions. This eliminates the need to provide theplurality of recessed portions. As a result, the impact on the magneticcircuit can be reduced if the projected and recessed portions aredistributed in the circumferential direction.

In the present embodiment, the motor housing 12 is provided. However,the motor housing can be omitted if the stator cores are clampedtogether axially by a fixing member such as bolts and a sealing memberis provided for each of the stator cores to prevent cooling water leak.This permits parts count reduction, thus providing an inexpensive pump.It is to be noted that the number of sealing members can be reduced byincreasing the number of areas integrally molded with resin.

Next, the features of the invention other than those described in theappended claims, which are understandable from the foregoingembodiments, will be described together with the effects thereof.

(1) A feature of the invention is an electric pump adapted to dischargea liquid and driven by an electric motor. The electric pump includes astator core having a coil wound therein and on which different magneticpoles are alternately formed on the inner periphery thereof as the coilis energized. The electric pump also includes a rotor adapted to rotatein a liquid and opposed to the magnetic pole forming portions of thestator core so that different magnetic poles are alternately formed inthe circumferential direction. The electric pump also includes a pumpstructural body adapted to discharge a liquid as it is given arotational force by the rotor. The electric pump also includesnon-magnetic partitions provided between the stator core and the rotorand integrally formed on the inner periphery of the stator core. Such aconstruction allows to form partitions where necessary and as many ofthem as necessary between the stator core and the rotor, providing asolution to the problem of the conventional electric motor whichrequires separate partitions between the stator core and the rotor. Thiswill permit size reduction.

(2) Another feature of the invention is an electric pump adapted todischarge a cooling medium and driven by an electric motor. The electricpump includes a stator core having a coil wound therein and on whichdifferent magnetic poles are alternately formed on the inner peripherythereof as the coil is energized. The electric pump also includes arotor adapted to rotate in a liquid and opposed to the magnetic poleforming portions of the stator core so that different magnetic poles arealternately formed in the circumferential direction. The electric pumpalso includes a pump structural body adapted to discharge a liquid as itis given a rotational force by the rotor. The electric pump alsoincludes channels, provided on the stator core, through which thecooling medium circulates in the stator core as the rotor rotates. Sucha construction ensures sufficient cooling of the stator coreirrespective of the electric motor construction, thus providing asolution to the problem of the prior art electric motor in whichsufficient cooling of the stator core cannot be achieved.

(3) Still another feature of the invention is an electric pump of claim5 having the motor and pump housings made of the same material. Such aconstruction ensures efficient heat transfer from the motor housing tothe pump housing.

1. An electric pump mounted in a vehicle, comprising: an electric motor,said electric motor including a core having a plurality of first clawmagnetic poles and a plurality of second claw magnetic poles, eachextending from both axial ends of one member of said core toward the endof another member of said core, said plurality of first claw magneticpoles and said plurality of second claw magnetic poles formedalternatively in the circumferential direction; a coil wound around andalong said core in a ring form, said coil generating different magneticpoles on said first and second claw magnetic poles as it is energized;and a magnetic pole member disposed to be opposed to said first andsecond claw magnetic poles and relatively rotatable with said core sothat different magnetic poles are formed in the circumferentialdirection; and a pump structural body adapted to discharge a flowingmedium as a rotational force is given to said pump structural body bysaid core or magnetic pole member.
 2. The electric pump of claim 1,wherein wherein said core is formed to include a single phase, andwherein magnetic field deviation portions are provided on said first andsecond claw magnetic poles to deviate a magnetic field in onecircumferential direction.
 3. The electric pump of claim 2, wherein saidmagnetic field deviation portions are provided so that onecircumferential side of said first and second claw magnetic poles isfarther from said magnetic pole member than the other circumferentialside thereof.
 4. The electric pump of claim 1, wherein said cores areformed to include a plurality of phases.
 5. An electric pump adapted todischarge a cooling medium, the electric pump comprising: an electricmotor, said electric motor including a coil wound in a ring form; a coreformed along said coil in a tubular form so that different magneticpoles are formed alternately in the circumferential direction as saidcoil is energized; and a magnetic pole member disposed to be opposed tosaid magnetic pole forming portions of said core and relativelyrotatable with said core so that different magnetic poles are formed inthe circumferential direction; and a pump structural body disposedadjacent to at least one end of said core and magnetic pole member sothat said pump structural body discharges a cooling medium as arotational force is given to said pump structural body by said core ormagnetic pole member.
 6. The electric pump of claim 5, wherein said coreand said magnetic pole member are housed in a motor housing; and whereinone axial end of said motor housing serves also as a pump housingadapted to house said pump structural body.
 7. The electric pump ofclaim 5, wherein the side end portion of said pump structural bodydisposed along the inner periphery of said motor housing is in closecontact with said core.
 8. The electric pump of claim 5, wherein arotation stop mechanism is provided between the side end portion of saidpump structural body disposed along the inner periphery of said motorhousing and said core to restrict the relative rotation of said core. 9.The electric pump of claim 8, wherein said rotation stop mechanismcomprises a projected portion on one side and a recessed portion on theother side.
 10. The electric pump of claim 8, wherein wherein said coresare formed to include a plurality of phases; and wherein said rotationstop mechanism is provided on said core for each phase.
 11. The electricpump of claim 5, wherein bearings for said magnetic pole member aredisposed along the inner periphery of said magnetic pole member.
 12. Anelectric pump adapted to discharge a liquid, the electric pumpcomprising: an electric motor, said electric motor including a coilwound in a ring form; a stator core formed along said coil in a tubularform and made from a compressed powder core so that different magneticpoles are formed alternately in the circumferential direction as saidcoil is energized, said core having a molded portion, formed by moldinga non-magnetic material, at least on the inner periphery thereof; and arotor disposed to be opposed to said magnetic pole forming portions ofsaid stator core so that different magnetic poles are formed in thecircumferential direction, said rotor rotating in a liquid; and a pumpstructural body adapted to discharge a liquid as a rotational force isgiven to said pump structural body by said rotor.
 13. The electric pumpof claim 12, wherein said non-magnetic material is a resin material. 14.The electric pump of claim 12, wherein said molded portion is providedover the entire inner periphery of said stator core.
 15. The electricpump of claim 12, wherein said non-magnetic material and said magneticpole are formed alternately on the inner peripheral surface of saidstator core.
 16. The electric pump of claim 12, wherein said statorcores are formed to include a plurality of phases; and wherein saidmolded portion is formed on said core for each phase.
 17. The electricpump of claim 12, wherein channels are provided on said molded portion.18. The electric pump of claim 17, wherein said channels are formedradially.
 19. The electric pump of claim 17, wherein said stator coresare formed to include a plurality of phases, wherein said molded portionis formed on said core for each phase, and wherein a channel is providedbetween said phases.
 20. The electric pump of claim 17, wherein saidchannel is formed at the center of said magnetic pole.